In recent years, along with enhancement of the operation rate of personal computers, and popularization of network infrastructure, as well as an increase in capacity of data storage and a decrease in its cost, occasions have increasingly occurred in which information such as documents and images, which have been provided in the form of paper printed matter, are received as simpler electronic information and viewed as received electronic information.
As viewing means for such electronic information, mainly employed are those of light emitting types such as conventional liquid crystal displays and CRTs or recent organic electroluminescence displays. Specifically, when electronic information includes document information, it is required to watch any of the above viewing means for a relatively long time. However, it is hardly stated that the above viewing means are human friendly. It is common knowledge that light emitting type displays result in problems such as eye fatigue due to flicker, inconvenient portability, limitations in reading posture, necessity to look at still images, or an increase in power consumption.
As means to overcome the above drawbacks, are known reflection type displays (having memory function) which utilize outside light and consume no power to maintain images. However, it is difficult to state that due to the following reasons, they exhibit sufficient performance.
Namely, a system employing polarizing plates, such as a reflection type liquid crystal, results in a problem for a white display due to a low reflectance of approximately 40%. In addition, it is difficulty to state that most methods to produce structuring members are simple and easy. Further, polymer dispersion type liquid crystals require high voltage and the contrast of the resulting images is insufficient due to utilizing the difference in refractive indices between organic compounds. Still further, polymer network type liquid crystals result in problems such as application of high voltage and requirement of complicated TFT circuitry to enhance memory capability. Yet further, display elements employing electrophoresis require high voltage of at least 10 V and tend to suffer insufficient durability due to aggregation of electrophoretic particles. Tin their principle, a bright white hue cannot be obtained due to coloring of filter by the former, and a dark black color cannot been obtained due to pattern color.
As one of the methods which enable a full color display, an electrochromic method has been know, which can be driven with a voltage of 3V or less. When a display exhibiting a bright white color, a high white-black contrast and a color display is prepared using an electrochromic method, it is necessary to laminate three layers each exhibiting a different color, resulting in a high cost due to the complicated element constitution. A full color electrochromic display having a flat color mixing structure has been known (for example, refer to Patent document 1). In this method, no fully sufficient white-black contrast has been obtained, since a dark black color cannot been obtained due to the flat color mixing structure. Also, a method to use a poly pyridine compound in an electrochromic display has been known (for example, refer to Patent document 2), however, in this method, only two colors can be displayed and, specifically, a black display cannot be obtained.
Patent Document 1: JP-A No. 2003-270670
Patent Document 2: Japanese patent No. 2930860